The instant invention relates to a seatbelt tension sensor system that employs a Villari effect sensor to measure tension in an automotive passenger restraint belt (seatbelt) application. Specifically, this invention provides a seatbelt tension sensor system which is rugged, insensitive to changes in temperature, and provides analog tension measurement at a high sampling rate.
The measurement of seatbelt tension is desirable in a wide variety of situations. Seatbelt tension measurements may be used to trigger seatbelt pretensioners, to modify airbag inflation profiles based upon the severity of a collision, and to measure any forward acceleration of a seat occupant, thereby allowing other collision related forces to be calculated. Additionally, seatbelt tension measurements may be used in conjunction with a seat weight sensor to ascertain the presence of an infant seat in an automobile.
A vehicle may contain automatic safety restraint actuators that are activated responsive to a vehicle crash for purposes of mitigating occupant injury. Examples of such restraint actuators include air bags, seatbelt pretensioners, and deployable knee bolsters.
One objective of an automatic safety restraint system is to mitigate occupant injury, thereby not causing more injury with the automatic restraint system than would be caused by the crash had the automatic restraint system not been activated. Notwithstanding the protective benefit of these automatic safety restraint actuators, there is generally both a risk and a cost associated with the deployment thereof. Generally, it is desirable to only activate automatic safety restraint actuators when needed to mitigate injury because of the expense of replacing the associated components of the safety restraint system, and because of the potential for such activations to harm occupants. This is particularly true of air bag restraint systems, wherein occupants too close to the air bag at the time of deploymentxe2x80x94i.e. out-of-position occupantsxe2x80x94are vulnerable to injury or death from the deploying air bag even when the associated vehicle crash is relatively mild. Moreover, occupants who are of small stature or with weak constitution, such as children, small adults or people with frail bones are particularly vulnerable to injury induced by the air bag inflator. Furthermore, infants properly secured in a normally positioned rear facing infant seat (RFIS) in proximity to a front seat passenger-side air bag are also vulnerable to injury or death from the deploying air bag because of the close proximity of the infant seat""s rear surface to the air bag inflator module.
Therefore, it is desirable to determine the presence of an infant seat in an automobile to inhibit the actuation of the airbag inflator. It has been demonstrated that when securing an infant seat to an automobile seat, seatbelt tension is often considerably higher than when adult or xe2x80x9cnormal sizedxe2x80x9d occupants are wearing the seatbelt. Individuals wearing seatbelts will rarely tighten a seatbelt above 10 pounds of seatbelt tension under normal operating conditions. In contradistinction, tests have shown that seatbelt tensions used to secure infant seats are as high as 50 pounds. In systems so equipped, high seatbelt tension can induce artificially high readings in a seat weight sensor by forcing the infant seat down into a seat pad used to sense the weight of an occupant on the seat. Therefore, when abnormally high seatbelt tension exists in combination with a high seat weight reading the presence of an infant seat may be deduced and the inflation profile of an airbag modified accordingly.
Known seatbelt tension measurement systems generally include spring-loaded contact sensors and load cells. Spring-loaded contact sensors provide only threshold weight detection, that is whether tension on the belt is above or below a certain threshold determined by the spring. Load cells provide moderately reliable analog tension measurement but are expensive, require periodic calibration, are easily damaged by off-axis loads, and have output readings that vary significantly with changes in temperature. Additionally, many load cell analog outputs signals are the product of an electronic summing junction that may induce time delays in obtaining a tension measurement thereby rendering the measurement unsuitable for a time-critical operation such as inhibiting the deployment of a passenger restraint.
In accordance with the present invention a seatbelt tension measurement system employing a Villari effect sensor is provided. This system provides a mechanism to transfer tensile force acting on the seatbelt to the Villari effect sensor thereby generating an electrical signal responsive to the amount of tension present in a seatbelt. A sensor housing is provided which encloses the Villari effect sensor and allows axial movement of a plunger acting thereon. The seatbelt tension sensor translates all of the tensile force acting on the seatbelt into compressive force acting on the Villari effect sensor while minimizing the effects of friction thereon.
The present invention provides a tension measurement system which is relatively uncomplicated in design, insensitive to variations in temperature, does not require periodic calibration, is not affected by off-axis loads, and can provide tension values at extremely high sampling rates. The instant invention also has the added advantage of being inexpensive to produce in comparison with, for example, load cell technology. Another feature of the instant invention is the ability to locate the sensor in several locations in the seatbelt system, depending on vehicle design requirements.
In addition, an electrical output provided by the present invention can be used to determine rates of deceleration in the event of a collision and can be used in concert with a seat weight sensor to determine the presence of an infant seat.
Accordingly, one object of the instant invention is to provide a seatbelt tension sensor that is capable of being incorporated into an airbag control system for determining the presence of an infant seat or other non-adult item in a vehicle seat.
Another object of the instant invention is to provide a seatbelt tension sensor that is rugged and insensitive to changes in temperature.
Yet another object of the instant invention is to provide a seatbelt tension sensor that is inexpensive to produce.
A yet further object of the instant invention is to provide a seatbelt tension sensor that may be placed in several positions within a vehicle seatbelt system depending on design requirements.
A yet further object of the instant invention is to provide a seatbelt tension sensor employing a Villari effect sensor to provide an analog tension indication to a passenger restraint control system.
The instant invention will be more fully understood after reading the following detailed description of the preferred embodiment with reference to the accompanying drawing figures.